1. Field of the Invention
The present invention is directed to the gripping of tubulars in the oil and gas well drilling industry, such as oil well piping and casing which can include rotating tubulars, holding tubulars fixed against rotation, and holding tubulars in a position, e.g. in a vertical position. In particular aspects, this invention relates to securely gripping an oil field tubular without significantly marking or damaging the tubular.
2. Description of Related Art
A variety of oil field apparatuses and devices are used to grip tubular members, in some cases while torque is being applied to a tubular member. For example, a variety of apparatuses use grippers (e.g. dies, gripping elements, and gripping members) to grip tubulars (such as casing, tubing, and pipe) including slips, elevators, spiders, clamps, tongs, backups and “chrome tools” used for gripping and/or rotating tubular members.
Power tongs in general have jaws which grip a tubular member. In several instances these jaws have a die member which is a sub-component of the jaw that contacts the tubular member. These dies can have ridges or teeth that contact and can cut into a tubular. In certain instances, there are five to eight teeth per linear inch formed across the gripping surface of a die which can bite into a tubular and prevent slippage between the tubular and the jaws when torque loads are applied to the tongs or the tubular.
Other apparatuses grip a tubular and hold the tubular in position, e.g. in position against vertical movement. The tubular can be part of a tubing, casing or drill string formed with a series of tubulars suspended above and/or in a wellbore. These apparatuses include, e.g., conventional slips, elevators, spiders, and safety clamps. Some slips and safety clamps use the weight of the tubular and/or string, and, in some cases, an external preload, to force gripping surfaces into contact with the tubular. In some cases, a gripping member of a slip has a gripping surface or gripping die on one face and an inclined plane on an opposite face. A slip holder, bowl or similar structure has a second and supplementary inclined surface positioned around the tubular with sufficient space between the tubular and slip bowl for the gripping member to be partially inserted between the slip bowl and tubular. Movement of the gripping member's inclined surface along the slip bowl's inclined surface moves the gripping surface to engage the tubular. In certain instances, the die or gripping surface of known slips is similar to that of tong jaw dies and the gripping surface has a series of steel teeth which bite into a tubular.
The teeth of known dies and gripping surfaces can leave deep indentations or gouges in the surface of the tubular which can adversely affect the structural integrity of the tubular member by causing a weak point in the metal which can render the tubular unsuitable for further use or can lead to premature failure of the tubular at a future date.
Die teeth made from carbon steel can introduce iron onto the surface of certain tubulars, e.g. a corrosion resistant alloy (CRA) tubular. Iron in a bite mark can act as a catalyst, causing a premature, rapid corrosion failure in the CRA tubular. This is also true for certain CWOR, completion and workover riser system tubulars.
Since many CRA materials such as stainless steel are work hardened materials, the malleability of the material can decrease after the material is mechanically stressed. Bite marks or indentations in stainless steel tubulars can produce localized “cold working” in the tubular so that points at which the marks are made are then less malleable than the other parts, creating weak points. Teeth in a uniform pattern can inflict bite marks which create a major stress riser which is more detrimental than a few individual random marks of similar depth, creating more damaging internal stresses in the tubular than a non-uniform pattern of bite marks.
In certain known systems, dies with smooth metal (e.g. aluminum) surfaces are used to engage a tubular. Such dies rely on a frictional grip and often employ significantly greater clamping forces than dies with teeth which can increase the risk that clamping forces damage a tubular. Also such aluminum surfaces can have an insufficiently high coefficient of friction to prevent slippage between the dies and the tubular at high torque loads or high vertical loads. To deal with this slippage, dies with fabric or screen in combination with an aluminum surface have been used. A carbide screen is placed between the tubular and the dies before the dies close upon the tubular. With the carbide screen, a substantially higher coefficient of friction can be developed between the dies and the tubular, but the screen is re-positioned between the tubular and die surface each time the dies grip and then release a tubular. In certain systems, instead of a separate screen, grit-faced (e.g. carbide or diamond) dies are used.
Many known dies have a fixed curvature which corresponds to the outer curvature of a tubular to be gripped or to a portion of this outer curvature. Depending on the outer curvature of the tubular to be gripped, these dies can have an uncertain gripping point(s) or grip center. A die whose gripping surface contacts a large portion of a relatively large tubular may contact only a minimal portion of a smaller tubular. It is also possible that minimal contact is achieved with much larger tubulars.
The prior art discloses a variety of tubular grippers; for example, and not by way of limitation, the following U.S. patent application and U.S. patents present exemplary systems and components thereof: U.S. Pat. Nos. 4,649,777; 5,291,808; 4,576,067; 7,036,397; 6,378,399; 7,204,173; 5,221,099; 7,231,984; 5,451,084; and 6,332,377—these applications and these patents all incorporated fully herein for all purposes.
The present inventors have recognized the need for a non-marking gripping die and methods of its use which provides a certain grip area or grip center. The present inventors have recognized the need for such a gripping die which does not damage a gripped tubular. The present inventors have recognized the need for a gripping die whose grip area is adjustable in use. The present inventors have recognized the need for a gripping die which can be used without manually placing a carbide cloth, screen or fabric adjacent the die.